import numpy as np
import pandas as pd
arr = np.arange(1,10).reshape(3,3)
df1 = pd.DataFrame(arr,columns=['a','b','c'])
df1.insert(0,'key',['001','003','002'])
print('左对象原始数据：\n',df1)
arr2 = np.arange(10,14).reshape(2,2)
df2 = pd.DataFrame(arr2,columns=['a','e'])
df2.insert(0,'key',['001','004'])
print('右对象原始数据df2：\n',df2)
df3=pd.merge(df1,df2,how='left')
print('左合并数据：\n',df3)
df4 = pd.merge(df1,df2,how='left',on='key')